The present invention relates to a printer, and more particularly, to the printer provided with a carriage drive control arrangement, the carriage having a print head mounted thereon.
There have been known ink jet printers with a print head formed with a plurality of jet nozzles. The print head is mounted on a carriage reciprocally movable in a print direction while maintained in confrontation with a print sheet. By ejecting ink from nozzles while using a carriage drive motor to drive the carriage in the print direction, an image can be formed out of dot patterns on the print sheet.
If a DC motor is used as the carriage drive motor, a circular encoder disk formed with a plurality of radial slits is attached to the DC motor.
A photosensor for determining timing of dot printing is provided in the printer. The photosensor includes a light emitting element and a light receiving element to transmit and receive light through the slits. The photosensor emits a pulse signal formed from alternating high and low level signals, which correspond to presence and absence of slits, and having a period equal to the sum of successive high and low level signals. The number of high and low level signals outputted from the photosensor is proportional to the distance moved by the carriage. Also, time duration of one period of the pulse signal indicates the speed of the carriage. By calculating these pulse signals, the print position of the carriage and the movement speed of the carriage can be determined so that timing of the dot printings can be determined.
At every rising edge and falling edge timing of the pulse signal, interrupt signal is inputted into a CPU of a control device. The control device computes the moving speed and the moving position of the carriage based on the pulse period and numbers of the pulses of the interrupt signal, so that the carriage drive motor is subjected to feed back control in order to permit the carriage drive motor to provide a predetermined speed mode including acceleration mode, constant velocity mode and deceleration mode. A pulse counter counts the pulse signal transmitted from the photosensor, and the CPU reads the count value.
If the carriage is driven for image recordation on the print sheet, a great number of pulse signals are generated in accordance with the movement of the carriage, and the pulse signals are inputted into the control device at every minute time period as a interrupt command. Therefore, the CPU of the control device receives the interrupt command at every minute time period, while the CPU also executes data processing for image printing. Accordingly, the CPU undergoes excessive load, and as a result, the image print processing may be delayed. In particular, if the carriage is moved at high speed for high speed printing, input pitch of the interrupt command is extremely short. Consequently, a CPU capable of high speed processing is required, which increases cost of the control device.